In this research, the influence of multi-walled carbon nanotubes (MWCNTs) on the fracture resistance of epoxy-based nanocomposites under out-of-plane shear (mode III) has been investigated experimentally and compared with their effect in the case of tensile (mode I) loading. Due to its wide industrial applications and low viscosity, epoxy LY-5052 has been used to manufacture the nanocomposite specimens. The MWCNT contents considered for nanocomposite samples are 0.1, 0.5 and 1.0 wt.%. Ultrasonic homogenization technique has been utilized for dispersing nano-fillers in the matrix resin. In order to measure the fracture resistance of pure epoxy and nanocomposite specimens under mode I and mode III loading conditions, a loading fixture recently developed for mixed mode I/III fracture tests has been employed. The obtained results show that in both loading conditions, increasing MWCNTs content up to 1.0 wt.% enhances the fracture resistance. However, the maximum values of mode I and mode III fracture toughness have been attained in nanocomposites containing 0.5 wt.% and 1 wt.% of MWCNT, respectively. Eventually, the observed trends in the experimental results have been discussed using the effective micro mechanisms of CNTs inside the polymer matrix.